The invention is based on a device for determining a rate rotation.
The use of rotation rate sensors that utilize the Coriolis effect is known in conjunction with systems for dynamic control in motor vehicles. Such rotation rate sensors typically comprise one or more masses that are set into mechanical oscillation at the frequency f.sub.s by an electrical oscillator circuit. These mechanical oscillations act on one or more acceleration sensors, which upon a rotation of the system also measure the Coriolis acceleration acting on the oscillating masses. From the excitation and acceleration signals, the rotation rate of the system can be determined with the aid of a suitable evaluation circuit.
An additional electrical test signal that is fed to the acceleration sensor or acceleration sensors can be used to cause an additional, arbitrarily generated acceleration to act upon the sensor. In this way, information on the properties of the acceleration sensor and the downstream evaluation circuits can for instance be obtained. It is thus also possible to detect errors, and especially systematic errors. This is especially important because rotation rate sensors that evaluate the Coriolis effect has systematic errors, whose effect on the measurement signal must be minimized by a suitable choice of evaluation method. Such systematic errors can be classified in one of the following types of error:
a) The acceleration sensor or sensors are sensitive not merely in the direction of the Coriolis acceleration to be measured but in other directions as well. PA1 b) The mechanical oscillator that is set into oscillation by the electrical circuit has unintended oscillation components in the direction of the Coriolis acceleration. PA1 c) Electrical feedthrough of the oscillation signal to the acceleration signal is possible.
To evaluate the output signals of rotation rate sensors, until now circuits have been used that are designed as analog circuits for signal processing. Such evaluation circuits, with which the rotation rate can be determined from the output signals of a rotation rate sensor and with which moreover monitoring the operability of the sensor or of the evaluation circuit is made possible, are described in International Patent Application WO 96/21138.
The known device for determining a rotation rate includes a rotation rate sensor which operates on the principle of a resonant oscillation gyrometer and is excited by means of an amplitude-regulated oscillator loop. This sensor is used for instance to ascertain the yaw speed of a vehicle. To that end, the effect of the Coriolis acceleration, which is a measure for the actual yaw speed, is evaluated. To monitor the operability of the sensor or of the associated electronics, an additional voltage, for instance in the form of a Bite function, is fed in at certain selectable times, and the reaction of the system to this additional voltage is evaluated for error detection.